I am trying to simulate light propagation on python using FFT following the Fresnel diffraction equation given on wikipedia:
Fresnel using fft (apologies can't post direct images)
The problem with this is that the output matrix from the DFT would be given in coordinates (p,q), which would inversely scale with my variable propagation distance z. To use the new (x,y) coordinates to account for the values outside of the FFT I would need to factor out at least the z value from my coordinate grid to get a 1-to-1 match, but doing so would increase my grid steps with increasing z.
What would be the normal solution to something like this?